The present invention relates to a depalletizing tool for an industrial robot, and more particularly to a gripping and transport clamp mounted at the end of a robotic arm. Furthermore, the present invention also relates to a method for operating the above-mentioned depalletizing tool.
Several manufacturing industries need to pack their product into boxes. These boxes are often shipped by the manufacturers, in an unfolded and stacked manner, on pallets. The piles of boxes need to be handled manually in order to transfer them from the pallet to a machine whose function is to form the boxes and to insert the product therein. The main problems to which are confronted these industries are the costs related to the use of manual labor and the industrial illnesses related to the repetitive handling of moderately heavy loads. Confronted to this type of problem, industrialists are turning themselves more and more towards automated solutions which replace human beings by an automated system.
An automated solution is generally defined as a set of mechanisms governed by a control system accomplishing a specific functionality. There exist on the market specialized systems capable of accomplishing depalletization work but only under very specific constraints. These constraints are such that the industries must consider robotized solutions which are much less constraining.
A robotized solution is defined as a system using an industrial robot with at least four degrees of freedom, as well as a tool specifically designed to be affixed on the robot and accomplish a very well defined task. There exist on the market robotized solutions capable of accomplishing depalletization work but the latter have certain constraints. These constraints are:
the pallets must always be placed at the same location;
the set of articles on the pallet must always be at the same location on the pallet;
the articles must be of the same dimension;
the piles of articles must be fastened individually, or the article must be a formed box; and
the tool of the robot or the downstream machine must remove the fasteners of the piles and dispose adequately of the fasteners (e.g. straps).
One can find on the market vision systems allowing the digitalization of objects in three dimensions. It is possible to adapt such a system to an industrial robot tool and to produce a computer program capable of processing the digital images and allowing a tridimensional tracing. Unfortunately, the costs involved would be prohibitive for an industrial application intended for a very competitive market.
Prehension is a very complex function even for human beings and there is no industrial robot tool presently on the market which is capable of carrying out, at a reasonable cost, such a complex task while remaining independent of the physical dimensions of the articles.
Known in the art, are, for example, U.S. Pat. Nos. 4,993,915 and 5,169,284 by Berger disclosing a row of claws for unstacking objects pilled up on a pallet. The claws are mounted on a carriage assembly movable horizontally on a guide rail. However, the use of this carriage assembly and guide rail reduces the independence with respect to the physical dimension and positioning of the articles.
A first object of the present invention is to provide a depalletizing tool for an industrial robot and method for operating the same which satisfy some of the above-mentioned needs and which are thus an improvement over what is known in the prior art.
According to the present invention, there is provided a gripping and transport clamp mounted at an end of a robotic arm being movable towards an object to be gripped, comprising:
a support member mounted at the end of the robotic arm;
a first lower pressing plate mounted on the support member, the first lower pressing plate being shaped for insertion under the object to be gripped;
sensor means adapted for detecting a reaction force being exerted on the first pressing plate upon displacement thereof;
first actuating means for inserting the first lower pressing plate under the object to be gripped in response to a detection of the reaction force by the sensor means;
a second lower pressing plate mounted below the first lower pressing plate on the support member, the second lower pressing plate being movable between a retracted position and an extended position;
second actuating means mounted between the second lower pressing plate and the support member for moving the second lower pressing plate between the retracted position and the extended position, thereby inserting the second lower pressing plate under the object to be gripped in response to the first lower pressing plate being inserted under the object to be gripped;
an upper pressing plate mounted on the support member, the upper pressing plate being movable toward the object to be gripped between an open position and a gripping position;
third actuating means mounted between the upper pressing plate and the support member for moving the upper pressing plate between the open position and the gripping position, thereby gripping the object between the upper and lower pressing plates; and
control means for receiving detection signals from the sensor means and for operating the actuating means.
According to the present invention, there is also provided a method for gripping an object with a clamp mounted at an end of a robotic arm, the clamp having a first lower pressing plate and second lower pressing plate below the first lower pressing plate, and an upper pressing plate, the method comprising the steps of:
sequentially moving the end of the robotic arm in horizontal step movements toward the object to be gripped and in vertical up and down step movements until the first pressing plate touches a separator positioned under the object to be gripped;
inserting the first lower pressing plate under the object to be gripped;
inserting the second lower pressing plate under the object to be gripped after the first lower pressing plate has been inserted under the object to be gripped; and
lowering the upper pressing plate toward the object to be gripped, thereby gripping the object between the upper and lower pressing plates.
According to the present invention, there is also provided a method for gripping an object with a clamp mounted at an end of a robotic arm, the clamp having a first lower pressing plate and second lower pressing plate below the first lower pressing plate, and an upper pressing plate, the method comprising the steps of:
moving the end of the robotic arm toward the object to be gripped until the first pressing plate is in proximity of the object to be gripped;
partially inserting the first lower pressing plate under the object to be gripped;
detecting if a reaction force exerted on the first lower pressing plate is below a predetermined threshold;
further inserting the first lower pressing plate under the object to be gripped if the reaction force exerted on the first lower pressing plate is below the predetermined threshold;
inserting the second lower pressing plate under the object to be gripped after the first lower pressing plate has been further inserted under the object to be gripped; and
lowering the upper pressing plate toward the object to be gripped, thereby gripping the object between the upper and lower pressing plates.
The invention as well as its numerous advantages will be better understood by the following non-restrictive description of a preferred embodiment made in reference to the accompanying drawings.